Vitamin K.sub.1 having the formula: ##STR1## and vitamins of the vitamin K.sub.2 series having the formula ##STR2## where n is an integer of from 1 to 13 are known in part as natural substances. These vitamin K series of compounds are used as additives for feedstuffs, for investigations of metabolism and other purposes. These compounds can be present, with reference to the first double-bond (viewed from the naphthoquinone ring) in the terpene chain, in Z-form (also called cis-form) or in E-form (also called trans-form) or as a mixture of these two forms. In biological investigations, the Z-form has proved to be biologically less active, if not even inactive. In the case of vitamin K, a "lack of biological activity" was ascertained for the cis-form in J. Nutr. 105:1519-1524, 1975. According to O. Isler in Angew. Chem., 71 (1959) No. 1., pages 13-15, in the case of substances of the vitamin K.sub.1 and K.sub.2 series, the mono-cis compounds (cis doublebond adjacent to the naphtoquinone ring system) showed a significantly lower activity than the all trans forms.
The efforts towards synthetic production of substances of the vitamin K.sub.1 and K.sub.2 series--the K vitamins influence the biosynthesis of prothrombin and other blood-coagulation factors--were indeed soon successful. Thus, a process for the manufacture of vitamin K.sub.1(20) starting from a methylnaphthohydroquinone and the corresponding terpene alcohol with a subsequent oxidation step was already described in 1939. There was obtained a total yield of 29%, based on phytol, without disclosing the E/Z ratios in the compounds obtained.
Recent processes, as disclosed e.g. in U.S. Pat. No. 2,683,176 or in German Patent Application No. 2,733,233, start from corresponding methyl-substituted naphthohydroquinone monoether derivatives, which are reacted with the corresponding terpene alcohols or terpene ethers and the resulting reaction products are oxidized. While in the former process there is obtained e.g. a yield of vitamin K.sub.1 of 37.5%, based on phytol, with a E/Z ratio of 90 to 92.5/7.5 to 10, the latter process leads only to the E-isomeric form with good yields of vitamin K.sub.1.
In other processes, methylnaphthohydroquinone and the respective terpene derivatives are condensed in the presence of metals such as zinc amalgam or zinc dust. In this case, the product is obtained in low total yields with the formation of E/Z-isomer mixtures. The use of N-sulphinylamines as the condensation agent has also been described, whereby, based on phytol, yields of vitamin K.sub.1 of only 4 to 7% have been obtained, but in the form of the pure E-isomers.
There exists thus a need for the provision of a process for the manufacture of compounds of the vitamin K.sub.1 and vitamin K.sub.2 series, in which these compounds are obtained in high yield and in a relatively simple manner. Since the synthesis of the specific methyl-substituted naphthohydroquinone derivative is expensive, the discovery of such processes in which this starting material need not be employed has been desired. In this case, it is especially desirable that such processes lead stereospecifically to the exclusively or predominantly biologically active E-form.